Combination process for upgrading naphtha

Abstract

A straight-run naphtha is fractionated at about 66° C., which is just below the boiling point of methylcyclopentane. The 66° C.+ fraction is reformed, and at least a portion of the reformate combined with the 66° C.- fraction and reacted under aromatization conditions over a ZSM-5-type catalyst to form a C 5 + product rich in aromatics. The C 5 + aromaticized product and the remaining reformate can be either sent for BTX recovery or used as a high-octane component of a gasoline blending pool.

What is claimed is: 
     
       1. A process for upgrading a naphtha-boiling-range hydrocarbon to useful products which comprises: (1) separating said naphtha just below the boiling point of methylcyclopentane into a light naphtha fraction containing C 6  paraffins and lower-boiling hydrocarbons and a heavy naphtha fraction containing methylcyclopentane and higher-boiling hydrocarbons;   (2) reforming said heavy naphtha fraction under reforming conditions to produce a reformate enriched in aromatic compounds compared with said heavy naphtha fraction;   (3) passing at least a portion of said reformate together with said light naphtha fraction in contact with a ZSM-5-type zeolite catalyst under aromatization conditions including a pressure from 0.5 to 68 atmospheres and a temperature from 343° to 649° C. to produce an aromatics-enriched effluent;   (4) separating said aromatics-enriched effluent into a C 4  - fraction and a C 5  + fraction; and   (5) recovering said C 5  + fraction as said product.   
     
     
       2. The process of claim 1 wherein the naphtha is a C 5  to C 8  straight-run naphtha and all of said reformate is passed in contact with said ZSM-5-type catalyst, and said product is sent for recovery of the benzene, toluene and xylene components therein. 
     
     
       3. The process of claim 1 wherein said reformate is separated into a first fraction boiling just below xylene and a second fraction containing xylene and higher-boiling components, said first fraction is said portion which is passed in contact with said ZSM-5-type catalyst, said product is sent for recovery of the benzene, toluene and xylene components thereof, and said second fraction is isomerized to optimize the xylene content thereof. 
     
     
       4. The process of claim 1 further comprising separating a C 3  /C 4  fraction from said aromatics-enriched effluent, and recycling said C 3  /C 4  fraction in contact with said ZSM-5-type catalyst. 
     
     
       5. The process of claim 1 wherein said ZSM-5-type catalyst is the Zn-H-ZSM-5 form. 
     
     
       6. The process of claim 1 wherein said ZSM-5-type catalyst is the H-ZSM-5 form. 
     
     
       7. The process of claim 1 wherein said aromatization conditions include a temperature from 500° to 540° C. and a pressure from 1 to 5 atmospheres, and no added hydrogen. 
     
     
       8. A process for upgrading a naphtha-boiling-range hydrocarbon to useful products, including a high-octane gasoline having a research octane number of at least 90 (Clear), which comprises: (1) separating said naphtha just below the boiling point of methylcyclopentane into a light naphtha fraction containing C 6  paraffins and lower-boiling hydrocarbons and a heavy naphtha fraction containing methylcyclopentane and higher-boiling hydrocarbons;   (2) reforming said heavy naphtha fraction under reforming conditions selected to increase the octane rating of the gasoline-boiling-range product;   (3) fractionating the product of the reforming operation into a light reformate which contains a substantial amount of C 7  - paraffins and a heavy reformate fraction which contains most of the toluene and the remaining high-boiling hydrocarbons;   (4) forming aromatics from said paraffins by passing said light reformate together with said light naphtha fraction in contact with a ZSM-5-type zeolite catalyst under aromatization conditions including a pressure from 0.5 to 35 atmospheres, a temperature from 454° to 556° C. and no added hydrogen and recovering an aromatics-enriched effluent from said aromatization operation;   (5) separating said aromatics-enriched effluent into a C 4  - fraction and a C 5  + fraction; and   (6) combining said C 5  + fraction with said heavy reformate to produce said high-octane gasoline.   
     
     
       9. The process of claim 8 further comprising separating a C 3  /C 4  fraction from said aromatics-enriched effluent and recycling said C 3  /C 4  fraction in contact with said ZSM-5-type catalyst.